Solid-state image sensor, method for producing solid-state image sensor, and electronic apparatus

ABSTRACT

A solid-state image sensor includes a semiconductor substrate having a photoelectric conversion element converting incident light into a charge and a charge retaining section temporarily retaining the charge photoelectrically converted by the photoelectric conversion element and a light shielding section having an embedded section extending in at least a region between the photoelectric conversion element and the charge retaining section of the semiconductor substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/582,203, filed Sep. 25, 2019, which is a continuation of U.S. patentapplication Ser. No. 15/589,999, filed May 8, 2017, now U.S. Pat. No.10,462,404, which is a continuation of U.S. patent application Ser. No.14/593,616, filed Jan. 9, 2015, now U.S. Pat. No. 9,659,984, which is acontinuation of U.S. patent application Ser. No. 13/606,828, filed Sep.7, 2012, now U.S. Pat. No. 8,964,081, which claims priority to JapanesePatent Application JP 2011-203337, filed in the Japan Patent Office onSep. 16, 2011, the entire disclosures of which are hereby incorporatedherein by reference.

BACKGROUND

The present technology relates to solid-state image sensors, methods forproducing the solid-state image sensor, and electronic apparatus and, inparticular, to a solid-state image sensor, a method for producing thesolid-state image sensor, and an electronic apparatus which make itpossible to obtain a better pixel signal.

In the past, a solid-state image sensor such as a CMOS (complementarymetal oxide semiconductor) image sensor and a CCD (charge coupleddevice) has been widely used in a digital still camera, a digital videocamera, and the like.

For example, the light that has entered a CMOS image sensor isphotoelectrically converted in a PD (photodiode) of a pixel. Then, thecharge generated in the PD is transferred to FD (floating diffusion) viaa transfer transistor and is converted into a pixel signal at a level inaccordance with the amount of received light.

Incidentally, in an existing CMOS image sensor, since a method by whichpixel signals are sequentially read from the pixels on a row-by-rowbasis (a so-called rolling shutter method) is generally adopted,distortion sometimes occurs in an image due to a difference in exposuretiming.

It is for this reason that Japanese Unexamined Patent ApplicationPublication No. 2008-103647, for example, discloses a CMOS image sensorthat adopts a method by which the pixel signals are read simultaneouslyfrom all the pixels by providing a charge retaining section in the pixel(a so-called global shutter method) and has an all-pixel simultaneouselectronic shutter function. By adopting the global shutter method, allthe pixels have the same exposure timing, making it possible to preventdistortion from occurring in the image.

Now, when a configuration in which the charge retaining section isprovided in the pixel is adopted, the layout of pixels is limited. Thismay decrease the aperture ratio, resulting in a reduction in thesensitivity of a PD and the capacity of the PD and the charge retainingsection. Furthermore, optical noise may be generated as a result of thelight entering the charge retaining section retaining the charge.

With reference to FIG. 1, the light that enters the charge retainingsection will be described. In FIG. 1, a sectional configuration exampleof one pixel of the CMOS image sensor is shown.

As shown in FIG. 1, a pixel 11 is formed of a semiconductor substrate12, an oxide film 13, a wiring layer 14, a color filter layer 15, and anon-chip lens 16 which are stacked. Furthermore, in the semiconductorsubstrate 12, a PD 17 and a charge retaining section 18 are formed. Inthe pixel 11, a region in which the PD 17 is formed is a PD region 19,and a region in which the charge retaining section 18 is formed is acharge retaining region 20. Moreover, in the wiring layer 14, a lightshielding film 21 having an opening in a region corresponding to the PD17 is provided.

In the pixel 11 configured as described above, the light that has beenconcentrated by the on-chip lens 16 and has passed through the colorfilter layer 15 and the wiring layer 14 passes through the opening ofthe oxide film 13 and illuminates the PD 17. However, as indicated withsolid-white arrows in FIG. 1, when the light is incident obliquely, thelight sometimes passes through the PD 17 and enters the charge retainingregion 20. If a charge generated as a result of the light that hasentered the charge retaining region 20 being photoelectrically convertedin the depth of the semiconductor substrate 12 leaks into the chargeretaining section 18 retaining the charge, optical noise is generated.

Moreover, in recent years, as disclosed in Japanese Unexamined PatentApplication Publication No. 2003-31785, for example, aback-illuminated-type CMOS image sensor has been developed. In theback-illuminated-type CMOS image sensor, since a wiring layer in a pixelcan be formed on the back (a side opposite to the side on which thelight is incident) of the sensor, it is possible to prevent thevignetting of the incident light caused by the wiring layer.

In FIG. 2, a sectional configuration example of one pixel of theback-illuminated-type CMOS image sensor is shown. Moreover, in FIG. 2,such components as are found also in the pixel 11 of FIG. 1 areidentified with the same reference characters, and their detaileddescriptions will be omitted.

As shown in FIG. 2, in a pixel 11′, the light illuminates the back side(a face facing an upper portion of FIG. 2) of the semiconductorsubstrate 12, the back side which is a side opposite to the front sideof the semiconductor substrate 12 on which the wiring layer 14 isprovided. Moreover, in the pixel 11′, the charge retaining section 18 isformed on the front side of the semiconductor substrate 12, and a lightshielding layer 22 having a light shielding film 21 is formed betweenthe semiconductor substrate 12 and the color filter layer 15.

In the pixel 11′ of the back-illuminated-type CMOS image sensorconfigured as described above, it is possible to increase thesensitivity of the PD 17. However, since the charge retaining section 18is formed on the front side of the semiconductor substrate 12, that is,the charge retaining section 18 is formed in a deep region of thesemiconductor substrate 12 for the incident light, it is difficult toprevent the leakage of light into the charge retaining section 18.

That is, as indicated with solid-white arrows in FIG. 2, the light thathas passed through the on-chip lens 16 at an angle sometimes leaks intothe charge retaining section 18 after passing through the opening of thelight shielding film 21, the opening formed above the PD region 19. Ifthe light leaks into the charge retaining section 18 retaining thecharge, optical noise is generated.

SUMMARY

As described above, in a configuration in which a charge retainingsection is provided in a pixel, since a PD is made smaller in size, thesensitivity of the PD is reduced, and optical noise is sometimesgenerated as a result of the light leaking into the charge retainingsection retaining the charge. This makes it difficult to obtain a goodpixel signal.

It is desirable to make it possible to obtain a better pixel signal.

A solid-state image sensor according to an embodiment of the presenttechnology includes: a semiconductor substrate having a photoelectricconversion element converting incident light into a charge and a chargeretaining section temporarily retaining the charge photoelectricallyconverted by the photoelectric conversion element; and a light shieldingsection having an embedded section extending in at least a regionbetween the photoelectric conversion element and the charge retainingsection of the semiconductor substrate.

A production method according to another embodiment of the presenttechnology includes: forming, on a semiconductor substrate, aphotoelectric conversion element converting incident light into a chargeand a charge retaining section temporarily retaining the chargephotoelectrically converted by the photoelectric conversion element; andforming a light shielding section having an embedded section extendingin at least a region between the photoelectric conversion element andthe charge retaining section of the semiconductor substrate.

An electronic apparatus according to still another embodiment of thepresent technology includes a solid-state image sensor including asemiconductor substrate having a photoelectric conversion elementconverting incident light into a charge and a charge retaining sectiontemporarily retaining the charge photoelectrically converted by thephotoelectric conversion element and a light shielding section having anembedded section extending in at least a region between thephotoelectric conversion element and the charge retaining section of thesemiconductor substrate.

According to the embodiment of the present technology, the photoelectricconversion element and the charge retaining section are formed on thesemiconductor substrate, and the light is blocked by the light shieldingsection having the embedded section extending in at least a regionbetween the photoelectric conversion element and the charge retainingsection.

According to the embodiment of the present technology, it is possible toobtain a better pixel signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a sectional configuration example of anexisting pixel;

FIG. 2 is a diagram showing a sectional configuration example of anexisting pixel in a back-illuminated-type CMOS image sensor;

FIG. 3 is a block diagram showing a configuration example of asolid-state image sensor to which an embodiment of the presenttechnology is applied;

FIG. 4 is a circuit diagram showing a configuration example of a pixel;

FIG. 5 is a diagram showing a planar configuration example of the pixel;

FIG. 6 is a sectional view showing a first configuration example of thepixel;

FIG. 7 is a diagram showing a planar configuration example of a lightshielding section;

FIG. 8 is a diagram illustrating a first process;

FIG. 9 is a diagram illustrating a second process;

FIG. 10 is a diagram illustrating a third process;

FIG. 11 is a diagram illustrating a fourth process;

FIG. 12 is a diagram illustrating a fifth process;

FIG. 13 is a diagram illustrating a sixth process;

FIG. 14 is a diagram illustrating a seventh process;

FIG. 15 is a diagram illustrating an eighth process;

FIG. 16 is a sectional view showing a second configuration example ofthe pixel;

FIG. 17 is a sectional view showing a modified example of the secondconfiguration example of the pixel;

FIG. 18 is a diagram showing a planar configuration example of the lightshielding section;

FIG. 19 is a sectional view showing a third configuration example of thepixel;

FIG. 20 is a sectional view showing a fourth configuration example ofthe pixel;

FIG. 21 is a sectional view showing a fifth configuration example of thepixel;

FIG. 22 is a sectional view showing a modified example of the fifthconfiguration example of the pixel;

FIG. 23 is a sectional view showing a sixth configuration example of thepixel;

FIG. 24 is a sectional view showing a seventh configuration example ofthe pixel; and

FIG. 25 is a block diagram showing a configuration example of an imagingdevice which is installed in an electronic apparatus.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, a specific embodiment according to the present technologywill be described in detail with reference to the drawings.

FIG. 3 is a block diagram showing a configuration example of asolid-state image sensor to which an embodiment of the presenttechnology is applied.

In FIG. 3, a solid-state image sensor 31 is a CMOS solid-state imagesensor and includes a pixel array section 32, a vertical drive section33, a column processing section 34, a horizontal drive section 35, anoutput section 36, and a drive control section 37.

The pixel array section 32 has a plurality of pixels 41 arranged in anarray, and the pixels 41 are connected to the vertical drive section 33via a plurality of horizontal signal lines 42 based on the number ofrows of the pixels 41 and are connected to the column processing section34 via a plurality of vertical signal lines 43 based on the number ofcolumns of the pixels 41. That is, the pixels 41 of the pixel arraysection 32 are disposed at the points of intersection of the horizontalsignal lines 42 and the vertical signal lines 43.

The vertical drive section 33 sequentially supplies drive signals (atransfer signal, a selection signal, a reset signal, and the like) fordriving the pixels 41 to each of the rows of the pixels 41 of the pixelarray section 32 via the horizontal signal line 42.

The column processing section 34 extracts the signal level of a pixelsignal output from each pixel 41 via the vertical signal line 43 byperforming CDS (correlated double sampling) on the pixel signal andacquires pixel data in accordance with the amount of received light ofthe pixel 41.

The horizontal drive section 35 sequentially supplies, to the columnprocessing section 34, drive signals for making the column processingsection 34 output the pixel data acquired from each pixel 41 for each ofthe columns of the pixels 41 of the pixel array section 32.

To the output section 36, the pixel data is supplied from the columnprocessing section 34 with timing in accordance with the drive signalsof the horizontal drive section 35, and the output section 36 amplifiesthe pixel data, for example, and outputs the amplified pixel data to animage processing circuit in a next stage.

The drive control section 37 controls the driving of each block in thesolid-state image sensor 31. For example, the drive control section 37generates a clock signal in accordance with the drive cycle of eachblock and supplies the clock signal to the block.

FIG. 4 is a circuit diagram showing a configuration example of the pixel41.

As shown in FIG. 4, the pixel 41 includes a PD 51, a first transfertransistor 52, a second transfer transistor 53, a charge retainingsection 54, FD 55, an amplification transistor 56, a selectiontransistor 57, and a reset transistor 58.

The PD 51 receives the light illuminating the pixel 41 and generates andstores a charge in accordance with the amount of the received light.

The first transfer transistor 52 is driven in accordance with thetransfer signal supplied from the vertical drive section 33. When thefirst transfer transistor 52 is turned on, the charge stored in the PD51 is transferred to the charge retaining section 54.

The second transfer transistor 53 is driven in accordance with thetransfer signal supplied from the vertical drive section 33. When thesecond transfer transistor 53 is turned on, the charge stored in thecharge retaining section 54 is transferred to the FD 55.

The charge retaining section 54 stores the charge transferred from thePD 51 via the first transfer transistor 52.

The FD 55 is a floating diffusion region having a predeterminedcapacity, the floating diffusion region formed at a connection pointbetween the second transfer transistor 53 and a gate electrode of theamplification transistor 56, and stores the charge transferred from thecharge retaining section 54 via the second transfer transistor 53.

The amplification transistor 56 is connected to a power supply VDD (notshown) and outputs a pixel signal at a level based on the charge storedin the FD 55.

The selection transistor 57 is driven in accordance with the selectionsignal supplied from the vertical drive section 33. When the selectiontransistor 57 is turned on, the pixel signal which is output from theamplification transistor 56 can be read into the vertical signal line 43via the selection transistor 57.

The reset transistor 58 is driven in accordance with the reset signalsupplied from the vertical drive section 33. When the reset transistor58 is turned on, the charge stored in the FD 55 is discharged to thepower supply VDD via the reset transistor 58, and the FD 55 is reset.

In the solid-state image sensor 31 having the pixel 41 configured asdescribed above, the global shutter method is adopted, and it ispossible to make all the pixels 41 transfer a charge to the chargeretaining section 54 from the PD 51 at the same time and allow all thepixels 41 to have the same exposure timing. This makes it possible toprevent distortion from occurring in the image.

FIG. 5 is a diagram showing a planar configuration example of the pixel41.

As shown in FIG. 5, in the pixel 41, the PD 51, the charge retainingsection 54, and the FD 55 are disposed on a plane surface. As a resultof the charge retaining section 54 being provided in the pixel 41 asjust described, the area of the PD 51 becomes small, which may reducethe sensitivity of the PD 51. Therefore, to increase the sensitivity ofthe PD 51, the solid-state image sensor 31 adopts aback-illuminated-type structure.

FIG. 6 is a diagram showing a sectional configuration example of thepixel 41 taken on the line VI-VI indicated with arrows of FIG. 5. InFIG. 6, a first configuration example of the pixel 41 is shown.

As shown in FIG. 6, the pixel 41 is formed of a wiring layer 61, anoxide film 62, a semiconductor substrate 63, a light shielding layer 64,a color filter layer 65, and an on-chip lens 66 which are stacked inthis order from a lower portion of FIG. 6. Moreover, in the pixel 41, aregion in which the PD 51 is formed in the semiconductor substrate 63 isa PD region 67, and a region in which the charge retaining section 54 isformed in the semiconductor substrate 63 is a charge retaining region68. Incidentally, the solid-state image sensor 31 is a so-calledback-illuminated-type CMOS image sensor in which the incident lightilluminates the back side (a face facing an upper portion of FIG. 6) ofthe semiconductor substrate 63, the back side which is a side oppositeto the front side of the semiconductor substrate 63 on which the wiringlayer 61 is provided.

The wiring layer 61 is supported by, for example, a substrate support(not shown) disposed under the wiring layer 61 and is formed of aplurality of wirings 71 performing, for example, reading of the chargeof the PD 51 formed in the semiconductor substrate 63 and an interlayerdielectric film 72, the wirings 71 which are embedded in the interlayerdielectric film 72. Moreover, in the wiring layer 61, in a regionbetween the PD 51 and the charge retaining section 54, a gate electrode73 forming the first transfer transistor 52 is disposed on thesemiconductor substrate 63 with the oxide film 62 located between thegate electrode 73 and the semiconductor substrate 63. When apredetermined voltage is applied to the gate electrode 73, the chargestored in the PD 51 is transferred to the charge retaining section 54.

The oxide film 62 has insulation properties and insulates the front sideof the semiconductor substrate 63.

In the semiconductor substrate 63, an N-type region forming the PD 51and an N-type region forming the charge retaining section 54 are formed.Moreover, on the back side of the PD 51 and the charge retaining section54, a front pinning layer 74-1 is formed, and, on the front side of thePD 51 and the charge retaining section 54, a front pinning layer 74-2 isformed. Furthermore, in the semiconductor substrate 63, an inter-pixelseparation region 75 for separating a pixel 41 from another pixel 41lying next to the pixel 41 is formed in such a way as to surround thepixel 41.

The light shielding layer 64 is formed of a light shielding section 76made of a light-blocking material and a high-permittivity material film77, the light shielding section 76 embedded in the high-permittivitymaterial film 77. For example, the light shielding section 76 is made ofa material such as tungsten (W), aluminum (Al), and copper (Cu) and isconnected to a GND (not shown). The high-permittivity material film 77is made of a material such as silicon dioxide (SiO₂), hafnium oxide(HfO₂), tantalum pentoxide (Ta₂O₅), and zirconium dioxide (ZrO₂).

Moreover, the light shielding section 76 is formed of a lid section 76 adisposed in such a way as to cover the semiconductor substrate 63 and anembedded section 76b embedded in a vertical groove (a trench section 84of FIG. 12) formed in the semiconductor substrate 63 in such a way as tosurround the PD 51 and the charge retaining section 54. That is, the lidsection 76 a is formed in almost parallel with the layers forming thepixel 41, and the embedded section 76 b is formed to a predetermineddepth in such a way as to extend in a direction almost perpendicular tothe lid section 76 a.

Here, the embedded section 76 b of the light shielding section 76 isformed in the inter-pixel separation region 75 in such a way as tosurround the PD 51 and the charge retaining section 54. In addition tothis configuration, the embedded section 76 b of the light shieldingsection 76 may form the periphery of the charge retaining section 54 ormay be formed between the PD 51 and the charge retaining section 54.That is, the embedded section 76 b simply has to be formed at leastbetween the PD 51 and the charge retaining section 54 in such a way thatthe PD 51 and the charge retaining section 54 are separated by theembedded section 76 b.

Moreover, in the light shielding section 76, an opening 76 c for makingthe light enter the PD 51 is formed. That is, as in a planarconfiguration example of the light shielding section 76 shown in FIG. 7,the opening 76 c is formed in a region corresponding to the PD 51, andother regions such as regions in which the charge retaining section 54and the FD 55 are formed are shielded from the light by the lightshielding section 76.

In the color filter layer 65, filters that allow the lights ofcorresponding colors to pass therethrough are disposed for each pixel41. For example, filters that allow green, blue, and red lights to passtherethrough are disposed for each pixel 41 in a so-called Bayerpattern.

The on-chip lens 66 is a small lens for concentrating the incident lightentering the pixel 41 onto the PD 51.

As described above, the pixel 41 includes the light shielding section 76having the embedded section 76 b at least between the PD 51 and thecharge retaining section 54. As a result, as indicated with solid-whitearrows in FIG. 6, even when the light is incident obliquely and passesthrough the PD 51, the light can be blocked by the embedded section 76b. This makes it possible to prevent the light from leaking into thecharge retaining region 68. Therefore, it is possible to prevent thegeneration of optical noise which may be generated when the light leaksinto the charge retaining region 68.

Moreover, by forming the embedded section 76 b in such a way as tosurround the charge retaining section 54, it is possible to prevent thegeneration of optical noise even when the size of the charge retainingsection 54 is increased and ensure the full well capacity of the chargeretaining section 54 adequately. That is, in an existing configuration,to prevent the generation of optical noise, it is necessary to form asmall charge retaining section. However, forming a small chargeretaining section decreases the full well capacity. On the other hand,in the pixel 41, by blocking the light by the embedded section 76 b, itis possible to increase the volume of the charge retaining section 54and, for example, form the charge retaining section 54 from an area nearthe front side of the semiconductor substrate 63 to an area near theback side of the semiconductor substrate 63. This makes it possible toensure a sufficient full well capacity.

Furthermore, in the pixel 41, since a back-illuminated-type structure isadopted, it is possible to increase the sensitivity of the PD 51. Thismakes it possible to prevent a reduction in sensitivity caused as aresult of the area of the PD 51 having become small.

Therefore, in the solid-state image sensor 31 having the pixel 41, it ispossible to keep the sensitivity necessary for the PD 51 and prevent thegeneration of optical noise in the charge retaining section 54. Thisallows the charge retaining section 54 to secure a sufficient full wellcapacity. Thus, the solid-state image sensor 31 can obtain a betterpixel signal than that of an existing solid-state image sensor andobtain a low-noise pixel signal with a wide dynamic range even at a lowintensity of illumination, for example.

Next, with reference to FIGS. 8 to 15, a method for producing thesolid-state image sensor 31 having the pixel 41 will be described.

In a first process, as shown in FIG. 8, as in a method for producing acommon solid-state image sensor, high-concentration impurities areion-implanted into the semiconductor substrate 63 having an etchingstopper layer 81 to form the front pinning layer 74-2, the PD 51, thecharge retaining section 54, and the front pinning layer 74-1. Then,after the oxide film 62 is stacked on the front side of thesemiconductor substrate 63 and the gate electrode 73 is formed, thewiring 71 is formed every time the interlayer dielectric film 72 isstacked in a predetermined thickness. In this way, the wiring layer 61is formed.

In a second process, after an adhesive layer 82 is formed on the frontside of the wiring layer 61 and a support substrate 83 is bonded to theadhesive layer 82, the entire structure is inverted as shown in FIG. 9,and a face on the back side of the semiconductor substrate 63 ispolished by a physical polishing method.

In a third process, a layer located on the back side of the etchingstopper layer 81 of the semiconductor substrate 63 is etched by wetetching. At this time, etching is stopped by the etching stopper layer81 formed of high-concentration p-type impurities. In this way, theetching stopper layer 81 is exposed as shown in FIG. 10.

In a fourth process, after the etching stopper layer 81 is removed, theback side of the semiconductor substrate 63 is polished by CMP (chemicalmechanical polishing) method. By doing so, the back side of thesemiconductor substrate 63 is made thinner as shown in FIG. 11.

In a fifth process, after a resist is formed on the back side of thesemiconductor substrate 63, exposure and development of the resist layeris performed in such a way that an opening is formed in a region inwhich the embedded section 76 b of the light shielding section 76 shownin FIG. 6 is to be formed. Then, by performing dry etching using theresist layer as a mask, the trench section 84 shown in FIG. 12 isformed.

In a sixth process, the high-permittivity material film 77 is formed onthe side and bottom faces of the trench section 84 and the back side ofthe semiconductor substrate 63. Then, from the back side of thehigh-permittivity material film 77, the light shielding section 76 isformed on the face on the back side of the high-permittivity materialfilm 77 and the inside of the trench section 84. As a result, as shownin FIG. 13, the light shielding section 76 having the lid section 76 aformed on the back side of the high-permittivity material film 77 andthe embedded section 76 b formed inside the trench section 84 is formed.For example, the light shielding section 76 is formed by performing CVD(chemical vapor deposition) by using tungsten as a material.

In a seventh process, the light shielding section 76 is etched by dryetching. By doing so, the opening 76 c is formed as shown in FIG. 14.

In an eighth process, the high-permittivity material film 77 is stackedon the light shielding section 76 and planarized by using ALD (atomiclayer deposition) method, for example. Then, as shown in FIG. 15, thecolor filter layer 65 and the on-chip lens 66 are formed by using theusual method.

By the processes described above, it is possible to produce thesolid-state image sensor 31 having the pixel 41.

Next, with reference to FIG. 16, another embodiment of the pixel will bedescribed.

A pixel 41A shown in FIG. 16 differs from the pixel 41 of FIG. 6 in thata front-side light shielding section 91 is formed in such a way as tocover the front side (the side where the wiring layer 61 is located) ofthe PD region 67 and the charge retaining region 68. In other respects,the pixel 41A is the same as the pixel 41. It is to be noted that suchcomponents as are found also in the pixel 41 are identified with thesame reference characters as appropriate, and their detaileddescriptions will be omitted.

As is the case with the light shielding section 76, the front-side lightshielding section 91 can block light and prevents the light illuminatingthe PD 51 from passing through the PD 51 and entering the wiring layer61. For example, in a configuration in which no front-side lightshielding section 91 is provided, when the light that has illuminatedthe PD 51 and entered the wiring layer 61 is reflected from the wiring71 in the wiring layer 61 and enters the charge retaining section 54retaining the charge, it is assumed that optical noise is generated bythe light.

Therefore, by providing the front-side light shielding section 91, thelight illuminating the PD 51 is prevented from passing through the PD 51and entering the wiring layer 61. This makes it possible to prevent thegeneration of optical noise and obtain a better pixel signal.

Next, with reference to FIGS. 17 and 18, a modified example of the otherembodiment of the pixel will be described.

A pixel 41A′ shown in FIG. 17 differs from the pixel 41A of FIG. 16 inthat a front-side light shielding section 91′ is formed in such a way asto cover the front side (the side where the wiring layer 61 is located)of the charge retaining region 68. In other respects, the pixel 41A′ isthe same as the pixel 41A. It is to be noted that such components as arefound also in the pixel 41A are identified with the same referencecharacters as appropriate, and their detailed descriptions will beomitted.

The front-side light shielding section 91′ has an opening 91a formed ina region corresponding to the PD 51, and, as is the case with thefront-side light shielding section 91 of FIG. 16, the front-side lightshielding section 91′ is formed in such a way as to shield the frontside of the charge retaining section 54 from light. Specifically, asshown in FIG. 18, although the front-side light shielding section 91′has the opening 91a formed in a region corresponding to the PD 51 andhas an opening for allowing various through electrodes to pass, thefront-side light shielding section 91′ is formed in such a way as tocover the charge retaining section 54 completely.

By providing such a front-side light shielding section 91′, it ispossible to prevent the light reflected from the wiring 71 in the wiringlayer 61 from entering the charge retaining section 54 even when thelight illuminating the PD 51 passes through the PD 51 and enters thewiring layer 61. Therefore, it is possible to prevent the generation ofoptical noise and obtain a better pixel signal.

Next, with reference to FIG. 19, still another embodiment of the pixelwill be described.

A pixel 41B shown in FIG. 19 differs from the pixel 41 of FIG. 6 in thata light shielding section 92 having an embedded section embedded in thesemiconductor substrate 63 from the front side (the side where thewiring layer 61 is located) of the semiconductor substrate 63 is formedin such a way as to extend therefrom. In other respects, the pixel 41Bis the same as the pixel 41. It is to be noted that such components asare found also in the pixel 41 are identified with the same referencecharacters as appropriate, and their detailed descriptions will beomitted.

The light shielding section 92 is provided in a portion other than atransfer region provided between the PD 51 and the charge retainingsection 54. By providing the light shielding section 92, it is possibleto prevent the leakage of light into the charge retaining section 54more effectively and prevent the generation of optical noise.

Next, with reference to FIG. 20, yet another embodiment of the pixelwill be described.

In FIG. 20, a sectional view of a pixel 41C including a portion in whichthe FD 55 is formed is shown. The pixel 41C differs from the pixel 41 ofFIG. 6 in that the embedded section 76 b is formed in such a way that alight shielding section 76-1 surrounds the FD 55. In other respects, thepixel 41C is the same as the pixel 41. It is to be noted that suchcomponents as are found also in the pixel 41 are identified with thesame reference characters as appropriate, and their detaileddescriptions will be omitted.

As shown in FIG. 20, in the pixel 41C, an n-type contact region 93 isformed on the front side of a p-type region forming the FD 55, and thecontact region 93 is connected to the wiring 71 via a contact section94. Moreover, in a region between the charge retaining section 54 andthe FD 55, a gate electrode 95 forming the second transfer transistor 53is disposed on the semiconductor substrate 63 with the oxide film 62located between the gate electrode 95 and the semiconductor substrate63.

The light shielding section 76-1 includes the lid section 76 a disposedin such a way as to cover the semiconductor substrate 63 and theembedded section 76b embedded in a vertical groove formed in thesemiconductor substrate 63 in such a way as to surround the PD 51, thecharge retaining section 54, and the FD 55.

As described above, the light shielding section 76-1 can adopt aconfiguration in which the FD 55 is also surrounded with the embeddedsection 76 b. This makes it possible to prevent the generation ofoptical noise more effectively.

Next, with reference to FIG. 21, yet another embodiment of the pixelwill be described.

A pixel 41D shown in FIG. 21 differs from the pixel 41 of FIG. 6 in thata light shielding section 76-2 is formed of the lid section 76 a and theembedded section 76 b, which are separated from each other. In otherrespects, the pixel 41D is the same as the pixel 41. It is to be notedthat such components as are found also in the pixel 41 are identifiedwith the same reference characters as appropriate, and their detaileddescriptions will be omitted.

That is, in the pixel 41 of FIG. 6, the light shielding section 76 isformed in such a way that the lid section 76 a and the embedded section76 b are connected to each other. The lid section 76 a and the embeddedsection 76 b do not have to be connected to each other as describedabove. As long as the light incident in an oblique direction can beblocked by the embedded section 76 b, the lid section 76 a and theembedded section 76 b may be separated from each other as in the pixel41D and clearance may be provided between the lid section 76 a and theembedded section 76 b.

Next, with reference to FIG. 22, a modified example of the yet otherembodiment of the pixel will be described.

In a pixel 41D′ shown in FIG. 22, part of the lid section 76 a and theembedded section 76 b is separated and forms a light shielding section76-3, and an embedded section 76b′ disposed around the PD 51 isseparated from the lid section 76 a. In other respects, the pixel 41D′is the same as the pixel 41.

As described above, it is possible to adopt a configuration in which thelid section 76 a and the embedded section 76 b are separated (or part ofthe lid section 76 a and the embedded section 76 b is separated) to formthe light shielding section 76-3. Also with this configuration, it ispossible to prevent the leakage of light into the charge retainingsection 54 and prevent the generation of optical noise.

Next, with reference to FIG. 23, yet another embodiment of the pixelwill be described.

A pixel 41E shown in FIG. 23 differs from the pixel 41 of FIG. 6 in thata light shielding section 76-4 is formed in such a way that part of theembedded section 76 b penetrates the semiconductor substrate 63. Inother respects, the pixel 41E is the same as the pixel 41. It is to benoted that such components as are found also in the pixel 41 areidentified with the same reference characters as appropriate, and theirdetailed descriptions will be omitted.

The light shielding section 76-4 is formed in such a way that theembedded section 76 b in a region other than a region between the PD 51and the charge retaining section 54, that is, other than a region whichis a transfer path over which the charge is transferred from the PD 51to the charge retaining section 54, penetrates the semiconductorsubstrate 63. In other words, although it is difficult to form the lightshielding section in a region between the PD 51 and the charge retainingsection 54 because the region is used for transfer of charges, formingthe embedded section 76 b in a region other than the region between thePD 51 and the charge retaining section 54 makes it possible to preventeffectively the leakage of light into the charge retaining section 54from a region other than the PD 51 of the same pixel 41E. Incidentally,a method for forming the light shielding section in such a way as topenetrate the substrate is disclosed in detail in Japanese UnexaminedPatent Application Publication No. 2010-226126, which the applicant ofthe present technology filed.

Next, with reference to FIG. 24, yet another embodiment of the pixelwill be described.

A pixel 41F shown in FIG. 24 differs from the pixel 41 of FIG. 6 in thata vertical electrode 73′ is formed. In other respects, the pixel 41F isthe same as the pixel 41. It is to be noted that such components as arefound also in the pixel 41 are identified with the same referencecharacters as appropriate, and their detailed descriptions will beomitted.

As shown in FIG. 24, in place of the gate electrode 73 of the pixel 41of FIG. 6, the pixel 41F includes, as an electrode forming the firsttransfer transistor 52, the vertical electrode 73′ embedded from thewiring layer 61 toward the semiconductor substrate 63. Adopting such avertical electrode 73′ makes it easier to transfer the charge from thePD 51 to the charge retaining section 54 and makes it possible totransfer the charge more reliably.

Moreover, the vertical electrode 73′ is formed after a trench is formedby digging a hole on the front side of the semiconductor substrate 63, athrough film is formed, pinning is performed to remove the through film,and the oxide film 62 is formed.

Moreover, in addition to the back-illuminated-type CMOS solid-stateimage sensor, the solid-state image sensor 31 according to theembodiment of the present technology can be applied to afront-illuminated-type CMOS solid-state image sensor. In this case, forexample, in the CMOS image sensor with the configuration shown in FIG.1, an embedded section of a light shielding film, the embedded sectionwhich extends in a nearly vertical direction in such a way as to connectto the light shielding film 21 and is embedded in the semiconductorsubstrate 12, is formed between the PD 17 and the charge retainingsection 18.

Incidentally, in the solid-state image sensor 31, to implement theglobal shutter, the charge retaining section 54 is provided and thecharges are transferred from the PDs 51 to the charge retaining sections54 concurrently. However, for example, a configuration in which nocharge retaining section 54 is provided and the charges are transferredfrom the PDs 51 to the FDs 55 concurrently may be adopted. In this case,the embedded section 76 b is formed in such a way as to surround the FD55.

Moreover, the solid-state image sensor 31 configured as described abovecan be applied to, for example, various kinds of electronic apparatussuch as an imaging system such as a digital still camera and a digitalvideo camera, a cellular telephone with an imaging function, or otherapparatus with an imaging function.

FIG. 25 is a block diagram showing a configuration example of an imagingdevice installed in an electronic apparatus.

As shown in FIG. 25, an imaging device 101 includes an optical system102, an image sensor 103, a signal processing circuit 104, a monitor105, and a memory 106 and can take a still image and moving images.

The optical system 102 is formed of one lens or a plurality of lenses.The optical system 102 guides the image light (the incident light) froma subject to the image sensor 103 and forms an image on alight-receiving surface (a sensor section) of the image sensor 103.

As the image sensor 103, the solid-state image sensor 31 of each of theconfiguration examples and modified examples described above is used. Inthe image sensor 103, electrons are accumulated for a certain period oftime in accordance with the image which is formed on the light-receivingsurface via the optical system 102. Then, a signal based on theelectrons accumulated in the image sensor 103 is supplied to the signalprocessing circuit 104.

The signal processing circuit 104 performs various kinds of signalprocessing on the signal charge output from the image sensor 103. Theimage (the image data) obtained as a result of the signal processinghaving been performed by the signal processing circuit 104 is suppliedto the monitor 105 and displayed thereon or supplied to the memory 106and stored therein (recorded thereon).

In the imaging device 101 configured as described above, by using, asthe image sensor 103, the solid-state image sensor 31 of each of theconfiguration examples and modified examples described above, it ispossible to obtain a better pixel signal and enhance image quality ascompared to the image quality obtained by an existing imaging device.

Incidentally, the embodiment of the present technology can also adoptthe following configuration.

(1) A solid-state image sensor including:

a semiconductor substrate having a photoelectric conversion elementconverting incident light into a charge and a charge retaining sectiontemporarily retaining the charge photoelectrically converted by thephotoelectric conversion element; and

a light shielding section having an embedded section extending in atleast a region between the photoelectric conversion element and thecharge retaining section of the semiconductor substrate.

(2) The solid-state image sensor according to (1) above, furtherincluding:

a wiring layer having a plurality of wirings; wherein

the light enters the photoelectric conversion element from a back sideof the semiconductor substrate, the back side opposite to a front sideof the semiconductor substrate on which the wiring layer is provided.

(3) The solid-state image sensor according to (1) or (2) above, wherein

the embedded section of the light shielding section is formed in such away as to surround the photoelectric conversion element and the chargeretaining section.

(4) The solid-state image sensor according to any one of (1) to (3)above, wherein the light shielding section further has a lid sectiondisposed in such a way as to cover at least the charge retaining sectionon the back side of the semiconductor substrate, the back side on whichthe light enters the photoelectric conversion element.

(5) The solid-state image sensor according to (4) above, wherein

in the lid section of the light shielding section, an opening is formedin a region corresponding to the photoelectric conversion element. (6)The solid-state image sensor according to any one of (1) to (3) above,wherein

the light shielding section further has a front-side lid sectiondisposed in such a way as to cover at least the charge retaining sectionon a front side of the semiconductor substrate opposite to a side onwhich the light enters the photoelectric conversion element.

(7) The solid-state image sensor according to (6) above, wherein

in the front-side lid section of the light shielding section, an openingis formed in a region corresponding to the photoelectric conversionelement.

It is to be understood that an embodiment is not limited to theembodiments described above and various changes can be made thereinwithout departing from the spirit of the present technology.

What is claimed is:
 1. A solid-state image sensor comprising: a semiconductor substrate having a photoelectric conversion element converting incident light into a charge and a charge retaining section temporarily retaining the charge photoelectrically converted by the photoelectric conversion element; and a light shielding section having an embedded section extending in at least a region between the photoelectric conversion element and the charge retaining section of the semiconductor substrate.
 2. The solid-state image sensor according to claim 1, further comprising: a wiring layer having a plurality of wirings; wherein the light enters the photoelectric conversion element from a back side of the semiconductor substrate, the back side opposite to a front side of the semiconductor substrate on which the wiring layer is provided.
 3. The solid-state image sensor according to claim 1, wherein the embedded section of the light shielding section is formed in such a way as to surround the photoelectric conversion element and the charge retaining section.
 4. The solid-state image sensor according to claim 1, wherein the light shielding section further has a lid section disposed in such a way as to cover at least the charge retaining section on a back side of the semiconductor substrate, the back side on which the light enters the photoelectric conversion element.
 5. The solid-state image sensor according to claim 4, wherein in the lid section of the light shielding section, an opening is formed in a region corresponding to the photoelectric conversion element.
 6. The solid-state image sensor according to claim 1, wherein the light shielding section further has a front-side lid section disposed in such a way as to cover at least the charge retaining section on a front side of the semiconductor substrate opposite to a side on which the light enters the photoelectric conversion element.
 7. The solid-state image sensor according to claim 6, wherein in the front-side lid section of the light shielding section, an opening is formed in a region corresponding to the photoelectric conversion element.
 8. A method for producing a solid-state image sensor comprising: forming, on a semiconductor substrate, a photoelectric conversion element converting incident light into a charge and a charge retaining section temporarily retaining the charge photoelectrically converted by the photoelectric conversion element; and forming a light shielding section having an embedded section extending in at least a region between the photoelectric conversion element and the charge retaining section of the semiconductor substrate.
 9. An electronic apparatus comprising: a solid-state image sensor including a semiconductor substrate having a photoelectric conversion element converting incident light into a charge and a charge retaining section temporarily retaining the charge photoelectrically converted by the photoelectric conversion element and a light shielding section having an embedded section extending in at least a region between the photoelectric conversion element and the charge retaining section of the semiconductor substrate. 